In recent years, higher color depth rather than the conventional eight bit color depth is more and more desirable in many fields, such as scientific imaging, digital cinema, high-quality-video-enabled computer games and professional studio and home theatre related applications. Accordingly, the state-of-the-art video coding standard H.264/AVC has already included Fidelity Range Extensions (FRExt), which support up to 14 bits per sample and up to 4:4:4 chroma sampling. The current SVC reference software JSVM does not support high bit depth.
However, none of the existing advanced coding solutions supports bit depth scalability. For a scenario with two different decoders, or clients with different requests for the bit depth, e.g. 8 bit and 12 bit for the same raw video, the existing H.264/AVC solution is to encode the 12-bit raw video to generate a first bitstream, and then convert the 12-bit raw video to an 8-bit raw video and encode it to generate a second bitstream. If the video shall be delivered to different clients who request different bit depths, it has to be delivered twice, e.g. the two bitstreams are put in one disk together. This is of low efficiency regarding both the compression ratio and the operational complexity.
The European Patent application EP06291041 discloses a scalable solution to encode the whole 12-bit raw video once to generate one bitstream that contains an H.264/AVC compatible base layer (BL) and a scalable enhancement layer (EL). The overhead of the whole scalable bitstream compared to the above-mentioned first bitstream is small compared to the additional second bitstream. If an H.264/AVC decoder is available at the receiving end, only the BL sub-bitstream is decoded, and the decoded 8-bit video can be viewed on a conventional 8-bit display device; if a bit depth scalable decoder is available at the receiving end, both the BL and the EL sub-bitstreams may be decoded to obtain the 12-bit video, and it can be viewed on a high quality display device that supports color depths of more than eight bit.